The invention relates to a device for actuating a fuel exchange valve of a reciprocating internal-combustion engine that is developed as a poppet valve. The invention is particularly directed to improvements in such devices where the poppet valve is moved between the open and closed positions against restoring spring forces.
A valve actuating device of this general type is known from European Patent (EP-PS) No. 0 118 591. Two electromagnets that are excited with respect to one another in a phase-shifted way form an oscillating system with two coil springs that, on both sides, rest against an armature disk attracted by the electromagnets. The poppet valve that is connected with the armature disk is moved back and forth in response to this oscillation and in the process opens or closes a fluid passage opening. When a device of this type is used for actuating a fuel-exchange poppet valve of a reciprocating internal-combustion engine, it is important that the mass of the spring system be kept as small as possible in order to, on the one hand, maintain a precise control over the whole speed range of the internal-combustion engine and, on the other hand, limit the energy requirement for the electromagnets to a minimal quantity.
It is therefore an objective of the invention to provide an electromagnetic actuating of the valve that works against the force of a spring and has moving spring masses that are as small as possible.
This objective is achieved by utilizing a torsion bar spring acting on the valve control lever. The torsion bar spring that is used for the actuating of the valve has no oscillating masses that negatively influence the oscillating system. Also the rocker lever that is connected rigidly with the torsion bar spring and is in operative connection with the poppet valve has only a very small reduced mass so that the armature coupled to the valve lever almost without inertia can follow the alternate excitations of the electromagnets and can control the poppet valve correspondingly.
A similar torsion bar spring is known from German Published Examined Application (DE-AS) No. 1 120 804 for a purely mechanical valve control that is actuated by a cam. However, the use of a torsion bar spring for an electromagnetic valve control has the decisive advantage that it becomes only properly effective by means of the elimination of the translationally moved spring masses and the corresponding reduction of the forces of inertia and with a still acceptable expenditure of energy, it can be operated for the electricity supply of the electromagnets.
In an advantageous development of the preferred embodiments of the invention, the torsion bar spring, at one of its ends, is connected in a torsionally fixed way with the valve control lever and is disposed in two bearing brackets that are arranged on both sides of the valve lever; while at the other end, the torsion bar, in a torsionally fixed way, is clamped into a holding bush that is screwed together with the cylinder head. The armature that is disposed so that it can be moved longitudinally centrically with respect to the two electromagnets is coupled to the valve lever in such a way that its distance to the logitudinal axis of the poppet valve is considerably smaller than its distance to the longitudinal axis of the torsion bar or the bearing center of the valve lever. In this way, an adapted path translation can be achieved, from the valve lift of the poppet valve optimized according to thermodynamic aspects to the lifting motion of the armature that is useful for commercially available electromagnets.
Since the end positions of these two lifting motions always have tolerances that are caused by manufacturing, but since, on the other hand, a tight closing of the poppet valve is absolutely necessary also when the armature disk rests against one electromagnet, it is advantageous to provide an elastically flexible connection between the free end of the valve lever and the shaft of the poppet valve. For this purpose, the fork-shaped end of the valve control lever engages between a pressure disk resting on a shoulder of the valve shaft and a sliding sleeve that is guided longitudinally on the valve shaft, said sliding sleeve, by means of a coil spring, being supported against a holding bush fastened at the end of the valve shaft.
In order to dampen the impact of the valve disk on the valve seat when the poppet valve is closed, a hydraulic damping device is arranged above the valve shaft in the cylinder head. Several damping disks are disposed in an oil-filled cylindrical damping space. When the damping sleeve that is fastened at the upper end of the valve shaft penetrates into the damping space, the oil that is located between the damping disks is displaced through defined throttling spaces and thus causes a softer, quieter placing of the valve disk on the valve seat.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.